// Copyright (c) 2010 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/threading/thread_collision_warner.h"

#include "base/logging.h"
#include "base/threading/platform_thread.h"

namespace base {

void DCheckAsserter::warn()
{
    NOTREACHED() << "Thread Collision";
}

static subtle::Atomic32 CurrentThread()
{
    const PlatformThreadId current_thread_id = PlatformThread::CurrentId();
    // We need to get the thread id into an atomic data type. This might be a
    // truncating conversion, but any loss-of-information just increases the
    // chance of a fault negative, not a false positive.
    const subtle::Atomic32 atomic_thread_id = static_cast<subtle::Atomic32>(current_thread_id);

    return atomic_thread_id;
}

void ThreadCollisionWarner::EnterSelf()
{
    // If the active thread is 0 then I'll write the current thread ID
    // if two or more threads arrive here only one will succeed to
    // write on valid_thread_id_ the current thread ID.
    subtle::Atomic32 current_thread_id = CurrentThread();

    int previous_value = subtle::NoBarrier_CompareAndSwap(&valid_thread_id_,
        0,
        current_thread_id);
    if (previous_value != 0 && previous_value != current_thread_id) {
        // gotcha! a thread is trying to use the same class and that is
        // not current thread.
        asserter_->warn();
    }

    subtle::NoBarrier_AtomicIncrement(&counter_, 1);
}

void ThreadCollisionWarner::Enter()
{
    subtle::Atomic32 current_thread_id = CurrentThread();

    if (subtle::NoBarrier_CompareAndSwap(&valid_thread_id_,
            0,
            current_thread_id)
        != 0) {
        // gotcha! another thread is trying to use the same class.
        asserter_->warn();
    }

    subtle::NoBarrier_AtomicIncrement(&counter_, 1);
}

void ThreadCollisionWarner::Leave()
{
    if (subtle::Barrier_AtomicIncrement(&counter_, -1) == 0) {
        subtle::NoBarrier_Store(&valid_thread_id_, 0);
    }
}

} // namespace base
